In some fields, such as in the field of space technology for example, some pieces of equipment are subjected to thermal and/or mechanical stresses which impair their form stability and setting stability (the set of six parameters x, y, z, θx, θy, θz describing the relative position and orientation of two solids is called the setting). They must therefore be subjected to stress relaxation and/or to micropositioning. This is the case, for example, with the primary mirrors of telescopes, or with some spatial observation instruments, or again with gradiometers.
When such a piece of equipment is joined to another piece of equipment by means of a fixing device (or joint), its setting and form stabilities may also be disturbed by thermal and/or mechanical stresses which this other piece of equipment and/or its fixing device undergo. This is what the person skilled in the art calls interface deformation.
In order to limit these disturbances, which lead to deformations and/or displacements and/or rotations that notably prevent initially fixed stability performance from being maintained, passive fixing devices are generally used that have chosen flexibility in certain directions and are made of temperature-stable materials (such as carbon-resin composites for example).
These fixing devices may also comprise isostatic supports, such as those for example which ensure three-point holding using a passive fixing device such as those used for mirrors (notably described in the patent documents FR 97/13439 and FR 94/10710), an A-frame support or an X-frame support. But these isostatic supports may generate residual stresses due notably to design of the flexibilities at launch loads.
Passive thermal control devices may also be provided, for example of the MLI (multi-layer insulation) type, and/or active thermal control devices, such as heaters or heat pipes for example.
It is also possible to eliminate the mechanical stresses of integration at the nominal operating temperature by precisely clamping the equipment beforehand.
All these means employed to limit the disturbances undergone by equipment prove costly due to the complexity of their mechanical production and/or the integration methods they require.